Sleep sack



FIG. 1 is a front view of sleep sack showing my new design;

FIG. 2 is a rear view thereof;

FIG. 3 is a left side view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a top view thereof; and,

FIG. 6 is a bottom view thereof.

The dashed broken lines in the Figures represent stitching, which forms no part of the claimed design.

The dot-dash broken lines in the figures and the areas within the dot-dash lines show portions of the sleep sack that form no part of the claimed design.

The shade lines in the Figures, which appear as slanted parallel lines, show contour and not surface ornamentation. 

CLAIM The ornamental design for a sleep sack, as shown and described. 